The Biomechanics of Muscle Actions Instructor: Alan Wiest Presentation Objectives • Define biomechanics • Introduce lever systems • Differentiate among the types of muscle actions of the musculoskeletal system • Determine the torque requirements necessary to cause those muscle actions Terminology • Biomechanics- the application of mechanical principles to biological systems. – “the physics of human movement” • Applications for a trainer: – safety, technique, intensity, client diversity, research Mechanical and Anatomical Lever Examples Levers of the Musculoskeletal System • Muscles function by pulling against bones • Bones rotate about joints – transmit force through the skin to the environment (dumbbell, etc.) • Body movements primarily act through the bony levers of the skeleton. Lever System (5 components of a lever system) O FM MM MR > (FM)(MM) = (FR)(MR) < • • • • • O = fulcrum FM = muscle force FR = resistive force MM = moment arm of the muscle force MR = moment arm of the resistive force FR Muscle Actions • Isometric Muscle Action: – muscle stays the same length while under tension – contractile torque = resistive torque (FM)(MM) = (FR)(MR) Lever System • Torque Equation: (FR)(MR) FM = ? M M =1 0i n. (FM)(MM) > = < isometric FM = ? O MR = 36 in. FR = 40 lbs. Torque Equation • Solve for isometric action > (FM)(MM) = (FR)(MR) < (FM=?)(10in.) = (40lbs.)(36in.) (10 in.) (10 in.) FM = 144 lbs. Muscle Actions • Concentric Muscle Action: – muscle shortens while under tension – contractile torque > resistive torque – effort phase of dynamic exercises – lifting resistance up against gravity (FM)(MM) > (FR)(MR) Lever System • Torque Equation: (FM)(MM) > = < concentric FM > 144 lbs. (FR)(MR) O FM MM MR FR Muscle Actions • Eccentric Muscle Action: – muscle lengthens while under tension – contractile torque < resistive torque – negative phase of dynamic exercises – controlled lowering of resistance against gravity (FM)(MM) < (FR)(MR) Lever System • Torque Equation: (FM)(MM) > = < eccentric (FR)(MR) FM < 144 lbs. O FM MM MR FR Isometric Muscle Action -no movement -contractile torque = resistive torque Concentric Muscle Action -muscle shortens -contractile torque > resistive torque Eccentric Muscle Action -muscle lengthens -contractile torque < resistive torque QuickTime™ and a decompressor are needed to see this picture.